Self-regulating compression amplifier



sept 27, 1956 D. c. BEATTY SELF-REGULATING COD/[PRESSION AMPLIFIER Filed NOV. 6, 1965 DNN NN. mIzoFUwm RY N Wm T me .n C I A NY OB 4 fr go ll-H United States Patent O l 3,275,946 SELF-REGULATING COMPRESSION AMPLIFIER Donald C. Beatty, 2800 Overhill Road, Birmingham, Ala. Filed Nov. 6, 196,3, SerLNo. 321,783 7 Claims. (Cl. 330141) This yapplication is related to my copending applic-ation, Serial No. 129,211, tiled 2 August 1961, now Patent No. 3,182,137. g

In voice frequency transmission systems, the need has long existed for an ecient and automatic means kto cornpensate for system degradation resulting primarily from temperature and other climatic changes which occur in a continuous land cyclic-like manner. Signal level variations from such changes are particularly noticeable over systems having long metallic circuit conductors.

The magnitude of impedance variations in a communication system is partially dependent upon the physical circuit components. This includes, among other things, the size .and type of conductors (open wire or sheathed cable), type of insulators and air-,spacing between their supporting structures. By way o-f illustration, it is known that a change in resistance value of approximately ve (5) percent in such conductors will result in a temperature variation of 22 F. from the standard 55 F. normally used when computing characteristics of transmission circuits. By extrapolation, it can be readily understood that total line attenuation over moderate length wire circuits will result in a signal impulse lloss of at least 30 db. It is obvious, therefore, that satisfactory signal energy transmission cannot be maintained within the aid of suitable means to compensate for such variations.

Various kinds of line facilities .an-d apparatus have been utilized to minimize signal degradation resulting Afrom climatic changes. In some instances, it has been found necessary to utilize 4-wire circuits in order to maintain signal strength at asatisfactory level. -Iri such ari arrangement, a separate pair of conductors is used for transmission in each direction. However, in order to hold the transmitted intelligence at Ia satisfactory' signal level, it is common practice to install one-way amplifiers or repeaters at regular intervals in each circuit pair of the 4-Wire system. Also, long-wire circuits are usually -broken up into circuit units or sections of moderate length in order to better control the signal .amplitude over the system as a whole. AOne of the repeaters in each circuit section is usually a master regulating repeater for the section. The device is a complex electro-mechanical apparatus which employs the principle of the balance-d bridge. A portion of the latter, known as: pilot wire, functions yas one arm of the bridge. To be effective, the pilot wire must extend through the same -length of the section as the circuit to be regulated. For this and other undesirable characteristics, such an approach towards' sig'- nal level regulation is ineiiicient, complex, costly, and diliicult to maintain operative'.

`My present invention, a novel type of self-regulating compression ampliiier, resolves the above and other dericiencies normally associated with signal energy regulation in communication circuits. It is` a general object of the invention therefore to improve the operation of voice frequency transmission systems, particularly as regards the maintenance of satisfactory levels of signal intelligence transmitted over such systems. l p

To this end, the invention is arranged' to'be connectable to a communication circuit, and includes aV means to lreceive input signal energy, 4and to automatically amplify or reduce such energy and retransmit it into other communication circuits.

Another object of the invention is to render a device capable of acceptingthe input of voice frequencyv en- 3,275,946 Patented Sept. 27, 1966 ergy of greater or lesser magnitude and to automatically adjust the output magnitude of such energy to a preselected value.

A further object of the invention is to provide a signal energy regulating device which has in its input section a variable loss lmeans arranged to respond to changing levels in the magnitude of the input energy, yand with said variable loss means arranged in a manner effective to continually adjust the gain to pro-duce a substantially constant level .a-t the output side of the signal energy regulating device.

Another object of the invention is to regulate the variable loss means by a novel voltage yampliiier whose direct current output is arranged to vary in ratio to the magnitude of the input energy to the signal energy regulating device.

One object of the invention is to provide, in combination,kan eiicient three-stage signal energy amplier having the last stage arranged in `a push-pull configuration, and having means provided to automatically regulate its own 4output to .a predetermined level.

A further object is to attain these desirable characteristics while providing :a highly compact and maintenancefree, self-regulating compression-type amplie'r; the physical dimensions of which .are substantially smaller than those of other facilities heretofore devised yfor the same purpose. p A

Other objects will appear from the following description, the claims yappended thereto, and wherein:

` FIGURE l is a schematic representation of the invention; A v

JF-IGUR-El 1A is a schematic lview of a conventional power supply useable with the invention;

FIGURE 2 is a block diagram depicting the invention inconjunction with metallic conductor circuits extending between two terminal points of a communication system.

The detailed description presented hereinafter may be more readily understood with a Vfunctional -summary of the invention .at this time. With that objective in view, it is pertinent to rem-ark that the sole pur-pose of a communication system is to provide means for timely transmission of intelligence in a satisfactory manner. For full com- -prehension of the intelligence, it is desirable that it be delivered to the recipient with minimum distortion and at a relatively constant signal level. The apparatus which I have provided accomplishes this.

As previously recited, the magnitude of signal energy decreases in proportion to the length of the communication circuit. At lselected points 4of, the circuit the energy must be amplified to restore it to a satis-factory level. It is at `such locations that my apparatus may be used to great advantage. Again, under other conditions, the signal energy may be of va major magnitude an-d `a reduction thereof is desirable to prevent over-modulation, crosstalk or other objectionable characteristics. Here, too, the apparatus may -be used to like advantage to reduce the excessive level to one of appropriate value.

With reference now to FIGURE l of the drawing, terminals A-B and C-D have been provided as input and output terminals respectively. Signal energy, of small magnitude, input to A-B will be induced into Section A by transformer T1; This energy, without initial regulation, will Ibe induced into` Section B by'TZ. The energy will thelreupon be amplied yby Q1 and Q2 and portions of it will be conducted simultaneously to R26V of Section C via leads 9-14 and to the primary of T3' via lead 9. With only minute delay the energy appears at the ybase of Q6 of Section D. Following amplification by Q6, rectification to negative voltage by D10, it appeans at the -base of Q5 as bias voltage for that transistor and Q5 begins to conduct and draw current. Emitted viathe emitter of Q5 and lead 19 to D9, the resistive impedance ofthe latter istlus caused tol be reduced. With voltage retardation thereby minimized,

the current appears at the multiple diode arrangements of Sections A and C via leads 18 and 17. A slight delay in reaching the diodes of Section C is provided by R17 as a 'time constant in order to enable Section A to begin func- 'tioning prior to Section C.

Flow of current through D1, D2, D3, fand D4 of Section A reduces the impedance of those diodes thereby effecting a greater or lesser resistive shunt across leads 3 and 4. This shunt, functioning as a variable resistor or volume control across the input leads to the main amplifier, Sec- -tion B, thus effectively regulates the input and consequently the output of that amplifier. i

Within an inaudible few microseconds of the time the -above events occur the initial input energy is induced by 'T3 into the Q3-Q4 circuitry, amplied thereby, and emit- `of the input signal energy to terminals A and B, i.e., energy of greater magnitude receives more regulation than energy of lesser value. Thus arranged, signal energy of whatever value, input to terminals A-B will be emitted via output terminals C-D lat a relatively constant level. Further, the

'time constant of signal level regulation has been arranged to occur in a manner so as to be inaudible to the recipient of the transmitted intelligence.

It is believed apparent, from the above, that input energy of excessive magnitude will be automatically reduced to a satisfactory output level, .and that input energy of less than a satisfactory value will be automatically regulated upward to the desired value.

Referring now to FIGURE 2, rectangles E and G illus- .trate the terminal points of a Ll-conductor communications circuit, an ordinary telephone switching oice for example; while the rectangles F, F, H and H represent the invention. Duplicate 2oonductor metallic circuits .T-K and L-M connect the terminal points. Conductors J-K function ras the transmit circuit for the West Terminal E and as the receive circuit for the East Terminal G while conductors L-M function as the transmitcircuit 'for East Terminal G and as the receive circuit for the West Terminal E. The invention may be physically and electrically associated with the circuits I-K and L-M at appropriate intervals ofthe circuit path wherever it is desired to correct for signal energy loss due .to system attenuation.

It is believed suiiciently obvious as not to require other special illustration that the 'invention shall be connected to appropriate communication circuits, and that proper electric power shall be provided.

For clarification, the description of FIGURE l, which follows, has been sectionalized into four parts each of which contain essential components and circuitry of the principal functional areas of the invention.

SECTION A Input variable loss means This section of the invention, arranged as a novel-type of balanced 'impedance bridge, is provided to maintain an automatic regulation over the magnitude of signal energy input to the apparatus. Diodes D1, D2, D3, and D4, with associated components and circuitry, function as a variable resistor or input attenuator :and respond to to the changing -levels in the input signal energy in proportion to the magnitude of such changes.

In considering Section A in detail, the primary Winding of ltransformer T1 is connected with terminals A and B by leads 1 and 2 respectively. Terminals A and B serve as the input terminals to the invention and as a terminus of a communication circuit to which the apparatus may be connected. Signal energy input to terminals A and B will therefore appear in the primary winding of T1 and will be indu'ctvely passed into the secondary winding.

One terminal of the secondary winding of T1 `and one terminal of the primary Winding of transformer T2 are connected together by lead 3 which includes the series connected resistors R2-R4. The other terminal of .the secondary winding of T1 is connected to one terminal of the primary winding of T2 by lead 4 which includes the series connected resistors R3-R5.

The multiple diode arrangement of D1, D2, D3, and D4, connected as illustrated, constitutes a shunt circuit from lead 3 to lead 4 at points between R2-R4 and R3- RS respectively. The overall impedance Value of this arrangement varies in proportion to the current flow therethrough and thus may present a greater or lesser resistive connection between leads 3 and 4. A decrease Vin this resistive value causes a greater retardation of input signal energy.

It will be observed that the negative terminals -of D2 vand D4 are connected to the common ground and the positive terminalsV are connected to leads 3 and 4 respectively. It 'will also be observed .that the negative terminals of D1 and D3 are connected to leads 3 and 4 respectively and the positive terminals to lead 18. Lead 18 continues to a connection with the negative terminal of diode D9 and one terminal of resistor R18, the other terminal of which is connected to the common ground.

This constitutes :a ground-to-ground 'circuit loop over ,which current does not iiow until such current is emitted from the negative terminal of D9. An increase of current into lead 18 causes the impedance value of diode arrangement D1, D2, D3, and D4 to vary proportionately. This novel Section A circuitry is provided, in combina- SECTION B Main signal energy amplifier This section of the invention has been arranged as an eflicient three-stage amplifier and is provided, in combination, to receive input signal energy from Section A, amplify, then retransmit the same, at substantially a constant level into another communication circuit which may be connected to the output terminals C and D.

Signal energy present in the primary winding of T2 will be passed by induction int-o the secondary. One terminal of the latter is connected to ground, the other terminal `to lead 5. Lead 5, with capacitor C2 in series, is connected with lead 7 which terminates in connection with one terminal each of R7 and R9 and with the base element of transistor Q1. The other terminal of R9 is grounded while the other terminal of R7 is connected to lead 6. From that junction point, lead 6 continues to a connection withv one terminal each of R6, C1, and R8. The other terminal of R6 is connected with the negative power supply, the other terminal of C1 is grounded, while the other terminal of R8 is joined to lead 8 at .a point between its connection with the collector of Q1 and one terminal of C3. The resistor R10 connects the emitter of Q1 to the com-mon ground.

Lead 8 continues Ifrom a connection with the other terminal of C3 and terminates in a joint connection with one terminal each of R11, R12, and the base element of Q2. 4The emitter of Q2 is grounded via resistor R13. The collector of Q2 is connected to one terminal of the primary winding of T3 by lead 9. The other terminal of that winding is connected with the negative power supply.

To one terminal of the 'secondary winding of T3 is connected lead 10,l the base element of Q3, and one terminal of R14. Lead 10 continues from the other terminal of R14 and the collector of Q3 to a connection with one terminal of the primary winding of output transformer T4. Lead 11 connects the other terminal of the secondary winding of T3 (it will be observed that this winding is connected to ground at its center point) with the lbase element of Q4 and vwith one terminal of R16. The other terminal of R16 and the collector of Q4 are joined to the other terminal of the primary winding of T4 by a continuation of lead 11. The center point of that primary Winding is connected to the negative power supply. The emitter elements of Q3 and Q4 are connected by R15 whose adjustable center point terminal is grounded.

The secondary winding of T4 is connected by leads 12-13 to terminals C and D respectively. Terminals C and D serve as lthe output terminals of the invention and as a terminus of another communication circuit to which the invention may be connected.

SECTION C I have interposed the Section C arrangement between Sections B and D in order to momentarily retard the initial passage of small magnitude signal energy input from Section B to Section D. The Section C provision thus enables a slight delay in the deve-lopment of optimum performance 'by the Section D arrangement and, in -addition, helps to nullify the detrimental affect of spike or transient voltage on the Section A circuitry. All of these things are desirable in creating a proper regulation of the magnitude of input signal energy so that its subsequent emission from Section B as output signal energy will be at a substantially constant value.

With reference to FIGURE 1 of the drawing, Section C is electrically (lead 14) interposed between the Section B and D provisions and has another connection, lead 17, extending to a juncture with lead 18. Beginning at that point, the circuit continues via lead 17, resistor R17, and terminates in a connection with the positive terminals of D5 and'D7. (For reasons presented hereinafter, R17 is provided to slightly retard passage of current to diodes D5, D6, D7 and D8 until the same is first effective upon diodes D1, D2, D3, and D4 of Section A.) The negative terminals of D5 and D7 are connected to the positive terminals of D6 and D8 -by leads 15 and 16 respectively. Leads 1'5 and 16 terminate in connection with one -terminal each of the :primary winding of T5. The second- Iary winding of T5 is joined to lead 14 in shunt connection across R26, the latter being in series with lead 14.

SECTION D This section of Ithe invention is provided to maintain regulation of the Section A provision. I have constructed this in a novel manner as an alternating current amplifier, the output of which is rectified to direct current and utilized -as the control medium for regulation of the overall impedance value of Section A.

With reference to FIGURE 1, it will be Iobserved that the input circuit to the Section D arrangement is via lead 14 and the common ground. Lead 14 includes resistors R26, R25, and capacitor C8, connected in series in that order, land extends from a junction with lead 9 to a connection with t-he 'base element of Q6. Signal energy, emitted by the collector of Q2 into lead 9, will -appear simultaneously in lead 14. Following appropriate regulation of its magnitude by the Section C provision, the energy is conducted to the base ele-ment of Q6 by a continuation of -lead 14. The emitter of Q6 is connected to the common ground 'by resistor R22 which has the capacitor C6 in shunt connection. The lbase of Q6 is likewise connected to the common ground by resistor R23 and to the negative .power supply by R24. The collector of Q6 is connected to the negative power supply by lead 23 which includes the series connected resistor R21. lLead 23 is joined by lead 20 at a point 'between R21 and the Q6 collector. Lead 20 continues from this connection and includes junctures with the following elements in the order named: the series connected capacitor C7, lead 22, the series connected diode D10, lead 21, the series connected resistor R20, the base element of transistor Q5,

the series connected capacitor C4, and terminates in a with the common ground. Lead 22 also terminates in a connection with the common, ground but includes the series connected diode D11. The collector of Q5 is connected to the negative power supply by resistor R19. Lead 19, connected to the emitter of Q5, includes the series connected diode D9 and terminates in a juncture with lead 18.

As in the case of the multiple diode D1, D2, D3, and D4 arrangement of Section A, Ithe resistive impedance value Iof D9 varies in proportion to the amount of current flowing through that component, i.e., loW impedance with current flow, high impedance without.

With Q5 in a near quiescent state and drawing minimum current because of the absence of proper bias at the time (i.e., for example, when Q6 is not receiving input energy via lead 14 with 'subsequent'rectification of its emissions by D10), D9 offers high resistance tothe passage of insignificant current present in lead 19 from the negative power supply via'the collector, base, and emitter elements of Q5. However, with proper biasing of Q5 by negative voltage emissions of D10, Q5 then conducts, draws current, and emits same into the lead 19 from its emitter. With the flow of current through D9 thus arranged, its resistive impedance decreases, thereby, permitting less retardation to such curren-t flow. This current, conducted via leads 19 and 18 to D1, D2, D3, and D4 is thereupon effective upon the Section A provision. This is true also in the case of D5, D6, `D7, and D8 of Section C, the current flowing thereto from lead 18 via lead 17 and resistor R17. I have provided the latter to momentarily impede the functioning of Section C so as to enable Section A to reach optimum performance slightly in advance of Section C.

From the functional description -outlined in the two preceding paragraphs, it is obvious that the multiple diode arrangements of Sections A and C remain in a high resistive impedance status during periods when Q5 is quiescent and non-conducting. The shunt circuit path between leads 3 and 4, as presented by D1, D2, D3, and D4 during such periods, is one of high resistance, and consequently, has an insignificant affect upon the passage of signal energy over those leads. Again, the shunt circuit across the primary winding of T5, as presented by diodes D5, D6, D7, D8, and the leads V15 and 16, is likewise one of high Vresistance during such periods and, consequently, has an insignificant short-circuitng affect upon that winding. In selecting T5, I chose a type of transformer having high impedance primary and secondary windings. The secondary, in shunt connection across R26, therefore functions normally as a high resistance shunt across that component and because of this causes only an insignificant change in its actual resistance. With current flow through D6, D7, D8, and D9, however, the resistive impedance value of those diodes is reduced thus presenting a more effective shunt across the primary winding of T5. As is well known in the art, the effect upon the secondary winding will, because of reflection, cause its impedance to be reduced, thereby, creating a more effective short circuit shunt across R26. Signal energy lpresent in lead 14 will thereupon flow via the less resistive secondary winding rather than via the then higher resistive R26. This, from a functional standpoint, effectively removes that resistor from the circuit and reduces signal energy retardation via lead 14.

It is believed apparent that the invention is not necessarily confined to the specific use or uses thereof described above, since it may be utilized for any purpose to which it may be suited. Nor is the invention to be necessarily limited to the specific construction illustrated and described, since such construction is only intended to be illustrative of the principles of operation and the means presently devised to carry out said principles, it being considered that the invention comprehends any change in construction that may be permitted within the scope of the appended claims.

I claim: l1. For connection in a four-wire communications cir- -cuit of the type having a separate pair of conductors for Ythe transmission of signals in each direction, apparatus to sense, at the location of the installation of the apparatus in the circuit, variations of a transmitted signal from Aa pre-selected magnitude and to restore the signal automatically to .said magnitude for transmission beyond said location comprising:

(a) an input section including (l)V a pair of leads connectable to one of said pairs of conductorsto provide an input terminus, and (2) a plurality of rectiiiers in shunt across said leads; (b) a main amplifying section including (l) an output Aof terminus connectable to said conductors, (2) a line of signal transmission. extending from the input section to said output terminus, and (3) amplification means connected in said line to amplify a signal to a given magnitude in ratio to that of a signal input to the main section; (c) a signal-retard section including (l) a pair of second leads (2) a plurality of rectiliers in shunt across the second leads, and (3) resistance means having a connection to the shunt connection of the second named amplitiers; (d) an impedance control section including (l) `a secondline of signal transmission,

(2.) amplifying means connected in said second line, and (3) at least one rectiiier arranged to rectify to direct current the output of the second-named amplifying means; and loopl circuit extending from the first line of signal transmission to the rst named rectiers in series connection with the second line of signal transmission, said signal-retard section being connected across said loop circuit at a location between the impedance control section,

and the input and main sections. 2. For connection in a four-wire communications circuit of the type having a separate pair of conductors for the ltransmission of signals in each direction, apparatus to sense, at the location of the installation of the apparatus in the circuit, variations of a transmitted signal from a pre-selected magnitude and to restore the signal automatically to said magnitude for transmission beyond said location, comprising:

(a) an input section including (l) a pair of leads connectable to one of said pairs of conductors to provide an input terminus, and

(2) a plurality of rectifiers connected in shunt across saidleads and having a connection to ground;

(b) a main amplifying section including (l) an output terminus connectable to said conductors of the communications circuit for further transmission of a signal restored bythe apparatus to a given, pre-selected magnitude,

(2) first signal transmission means connected between the input section and said output terminus,

and

(3) amplification means connected in said means to amplify a signal to a given magnitude in ratio to the magnitude of a signal incoming to the main section;

(c) a signal-retard section including (1) a pair of second leads,

(2) a plurality of rectiiiers connected in shunt across the second leads and having va connection to ground,

(3) 'a third lead having a connection to the second named rectiiiers, and

(4) resistance means series-connected in the third lead; and

(d) an impedance control section including 1) second signal transmission means,

(2) amplifying means connected in the second transmission means for amplifying to a given magnitude a signal passing therethrough,

(3) means providing a connection between the respective signal transmission means and extend,- ing to a juncture with the second lea-ds,

(4) at least one rectifier arranged to' rectify to direct current the amplified output of the impcdance control section, and

(5) a connection between the iirst and last-named .rectifiers and having a juncture with the third lead.

3. For connection in a four-wire communications circuit of the type having a separate pair of conductors for the transmission of signals in each direction, apparatus to sense, at the location of the installation of the apparatus in the circuit, variations of a Itransmitted signal from a pre-selected magnitude and to restore the signal automatically to said magnitude for transmission beyond said location, comprising:

(a) an input section including (1) a pair of leads connectable to one of said pairs of conductors to provide an input terminus,

(2) iirst and second rectiiier means connected in shunt across said leads, and

(3) a connection extending from the second rectiier means to ground;

a main amplifying section -including (l) an output terminus connectable to said conductors of the communications circuit for further transmission of a signal restored by the apparatus to a given, pre-selected magnitude,

(2) a signal transmission line connected between the input section and the output terminus, and

(3) ampliiication means connected in said line to amplify a signal to a given magnitude in ratio to the magnitude of a signal incoming to the main section;`

(c) a signal-retard section including l) a pair of second leads,

(2) third and fourth rectifier means connected in shunt across said second leads,

(3) a connection between the fourth rectifier means and ground,

(4) a third lead connected to the shunt connection of the third rectifier means, and

(5) resistance means series-connected in the third lead; and

an impedance control section including (l) a second signal transmission line,

(2) amplifying means connected in the second line for amplifying to a given magnitude a signal passing therethrough,

(3) means providing a connection between said signal transmission lines and extending to a juncture with the respective second leads,

(4) fifth rectifier means series-connected in the second line of signal transmission and operative to lrectify theV ampliiied current output of the impedance control section to direct current, and

(5) means providing a connection between the first and fifth rectifier means and said thirdl lead. 4. For connection in a four-Wire communications circuit of the type having a separate pair of conductors for the transmission of signals in each direction, apparatus to sense, at the location of the installation of the apparatus in the circuit, variations of a transmitted signal from a pre-selected magnitude and to restore the signal 9 automatically to said magnitude for transmission beyond said location, comprising:

l(a) an input section including (1) a pair of leads connectable to one of said pairs of conductors to provide 4an input terminus,

(2)a pair of first and a pair of second rectifiers connected between said leads, and

(3) a connection from the second rectifiers to ground;

V(b) a main amplifying section including (l) an Voutput terminus connectable to said conductors of the `communications circuit for further transmission of a signal restored by the apparatu-s to said pre-selected magnitude,

(2) a signal transmission line connected between the input section and the output terminus, and

(3) amplification means connected in said line to amplify a signal to a given magnitude in ratio to the magnitude of a signal incoming to the main section;

(c) a signal-retard section including (l) a pair of second leads,

(2) a pair of third and a pair of fourth rectifiers connected across said second leads,

(3) a connection between the fourth rectifiers and ground,

(4) a third lead connected to the third rectifiers,

and

(5) resistance means connected in the third lead;

and

(d) an impedance control section including (l) a second signal transmission line,

(2) amplifying means connected in the second line for amplifying a signal passing therethrough to a given magnitude at the output end of the second line,

(3) a fourth lead connected between the first and second signal transmission lines, said second leads being connected to the fourth lead,

(4) a fifth rectifier series-connected in the second line for rectifying current amplified within the impedance control section to direct current, and

(5) a fifth lead connected between the first and fifth rectifiers and having a connection to the third lead.

5. For connection in a four-wire communications circuit of the type having a separate pair of conductors for the transmission of signals in each direction, apparatus to sense, at the location of the installation of the apparatus in the circuit, variations of a transmitted signal from a pre-selected magnitude and to restore the signal automatically to said magnitude for transmission beyond said location, com-prising:

(a) an input section including (1) a pair of leads connectable to one of said pairs of conductors to provide an input terminus,

(2) a first resistor connected in shunt across said leads,

(3) a plurality of second resistors 'connected in series in each of said leads,

(4) a pair of first and a pair of second rectifiers connected between said leads, and

(5) a connection from the second rectifiers to ground;

(b) a main amplifying section including (l) an output terminus connectable to said conductors of the communication circuit for further transmission of a signal received by the apparatus and restored thereby to the pre-selected magnitude, 1

(2) ia signal transmission line connected between the input section and the output terminus, and

(3) amplification means connected in said signal transmission line and arranged to amplify a signal passing therethrough to a given magnitude i() in ratio to the magnitude of the signal incoming to the main amplifying section;

(c) a signal-retard section including (1) a pair of second leads,

(2) a pair of third and a pair of fourth rectifiers yconnected across said second leads,

(3) a connection between the fourth rectiiiers and ground,

(4) a third lead connected at one end to the third rectifiers,

(5) a third resistor series-connected in the third lead, and

(6) a fourth resistor connected between the sec- -ond leads; and

(d) an impedance control section including (1) a second signal transmission line,

(2) amplifying means connected inthe second line and arranged to amplify a signal passing therethrough to `a given magnitude at the output end `of the second line in ratio to the magnitude of t `said signal when passed into the input end of the second line,

(3) a fourth lead connected between the first and second signal transmission lines, a portion of the fourth lead having the fourth resistor series connected therein and constituting the connection of the fourth resistor across the -second leads,

(4) a fifth rectifier series connected in the second line at the output end thereof for rectifying current amplified within the impedance control section to direct current, and

(5) -a fifth lead connected between the fifth and iirst rectifers, the third lead being connected to said iifth lead.

6. For connection in a four-wire communications circuit -of the type having a separate pair of conductors for the transmission of signals in each direction, apparatus to sense, at the location of the installation of the apparatus in the circuit, variations of a transmitted signal from apreselected magnitude and to restore the signal automatically to said magnitude for transmission beyond said location, comprising: v

(a) an input section including (l) a pair of leads connectable to one of saidpairs of conductors to provide an input terminus, t

(2) a first resistor connected in shunt across said leads,

(3) a pair of second resistors -connected in series in each of said leads,

(4) a pair of iirst and a pair of second rectiers connected in shunt across said leads at a location between the series-connected resistors, the first retifiers having their negative terminals connected to the respective leads and the second rectifiers having their positive terminals connected to the respective leads, and

(5 a connection extending to ground from a location between the respective second rectiers;

(b) a main amplifying section including (l) an output terminus connectable to said pair of conductors of the communication circuit for further transmission of a signal received by the apparatus and restored thereby to the preselected magnitude,

(2) a signal transmission line connected between the input section and the output terminus, and

(3) amplification means connected in said signal transmission line and arranged to amplify a signal passing therethrough to a given magnitude in ratio t-o the magnitude of said signal when passing into the main amplifying section from the input section;

(c) a signal-retard section including (1) a pair of second leads,

(2) a pair of third and a pair of fourth rectifiers connected in shunt across said second lead-s, the third rectifiers having their negative terminals connected lto one end of the respective second leads and Ithe fourth rectifiers having their posiconnected in shunt across said leads at a location between the series-connected resistors, the first rectifiers having their negative terminals of Vconductors of the communication circuit for further transmission of a signal received by the apparatus and restored thereby to the pre-selected magnitude,

. tive terminals connected to the respective sec- (2) a signal transmission line connected between ond leads, the second transformer and said output termil(3) a connection to ground extending from a locanus, and

tion between the fourth rectiers, (3) amplification means connected in said signal (4) a third lead connected at one end tothe posi transmission line and arranged to amplify a tive terminals of the third rectifiers, signal Vpassing therethrough to a given magni- (5) a'third resistor series connected in the third tude in ratio to lthe magnitude of said signal lead, and v when passed into the main amplifying section .(6) ya fourth resistor connected between the other from the input section;

ends of the second leads; and (c) a signal-retard section including (d) an impedance control section including y (l) apair of second leads,

(1) a second signal transmission line having input (2) a pair of third and a pair of fourth rectifiers V'and output ends, connected in shunt across said second leads, (2) amplifying means connected in said second the third rectifiers having their negative termi- ]ine and arranged to amplify a signal passing nals connected to one end of the respective therethrough to a given magnitude at the outsecond leads and the fourth rectifiers having i., put end of the second line in ratio to the magtheir positive terminals connected to the respecnitude of said signal when passed into the intive second leads, put end of the second line, (3) a connection extending Ito ground from a lo- (3) a fourth lead connected between the first sigcation between the fourth rectifiers,

.nal transmission line and the input end of the (4) a third lead connected at one end to the t second signal transmission line, `a portion of the positive terminals of the third rectifiers,

fourth lead having the fourth resistor series con- (5) a third resistor series-connected in the third nected therein and constituting the connection lead,

.of the' fourth resistor across the second leads, (6) a fOurtll reSiStOr ccnnecied between the other i (4)a fifth rectifier series connected in the second 30 ends ofthe Second leads, and

signal transmission line at the output end there- (7) a -tliird transformer COIlneCted between the of for rectifying current amplified within the second leads at a location between said other impedance control section to direct current, and endS Of the Second leads and the shunt of the (5) a fifth lead connected between the fifth rectifourth reCtllierS thereaCrOSS; and

fier and the positive terminals of the first recti- (d) an impedance ccntrOl Section including ners, the third lead being connected at its other (l) a SeeOnd Signal transmission line having inend to the fifth lead intermedia-te the ends of vPut aud Output endS, the fifth1ead t (2) amplifying means connected in said second 7,. For connection in a four-wire communications cirline and arranged t0 amplify n Signal Passing cuit of the type having a separate pair of conductors for 40 therethrough t0 a given magnitude at the Output r the transmission of signals in each direction, apparatus end 0f the Second line in ratio t0 the magnitude to sense, at the location of the installation of the appa- 0f Said Signal When passed into theinput end ratus in the circuit, variations of a transmitted signal 0f the Secund line, from a pre-selected magnitude and to restore the signal (3) n fOurtll lead Connected between the first automatically to said magnitude for transmission beyond s Signal transmission liue aud the input end 0f said location, comprising; v the second signal transmission line, a portion (a) aninput secrionincluding t of the fourth lead having the fourth resistor V(1) a pair 0f leads oonnectable at one end to one series-connected therein and constituting the of said pairs of conductors of said circuit to Connection 0f the fOurth reSiStOr across the secprovide an input terminus, 0nd leads, (2) a first transformer Connected between said (4) a fifth rectifier series-connected in the second leads, signal transmission line at the output end there- (3) a second transformer connected between said 9i for rectifying Current amplified Within the leads at the other ends thereof, lmpedance control section to direct current, and (4) a first resistor connected in shunt across said 55 (5) a llfth lead Connected between the fth recleads at a location between the transformers, -llei and 'the Positive terminals 0f the first rec- (5) a pair .of Second resistors Connected n Sel-ies tlfiers, the third lead being connected at its other in each of said leads at a location between said end t0 the llftll lead intermediate the ends of shunt and the second transformer, the ilftll lead- 4(6) a pair of first and a pair of second rectifiers 60 References Cited by the Examiner UNITED STATES PATENTS n 2,193,966 3/1940 connected to the respective leads and the sec- 3 210 5gg 10/1965 {siss ond rectlliers having their positive terminals con- 65 3:2261653 12/1965 'Miller :-"n 3,3() 141 nected to the respective leads, and (7) a connection extending to ground from a location between the second rectifiers; ('b) a main amplifying section including l(l) an output terminus connectable to said pair KATHLEEN H. CLAFFY, Primary Examiner. kH. ZELLER, Assistant Examiner. 

7. FOR CONNECTION IN A FOUR-WIRE COMMUNICATIONS CIRCUIT OF THE TYPE HAVING A SEPARATE PAIR OF CONDUCTORS FOR THE TRANSMISSION OF SIGNALS IN EACH DIRECTION, APPARATUS TO SENSE, AT THE LOCATION OF THE INSTALLATION OF THE APPARATUS IN THE CCIRCUIT, VARIATION OF A TRANSMITTED SIGNAL FROM A PRE-SELECTED MAGNITUDE AND TO RESTORE THE SIGNAL AUTOMATICALLY TO SAID MAGNITUDE FOR TRANSMISSION BEYOND SAID LOCATION, COMPRISING: (A) AN INPUT SECTION INCLUDING (1) A PAIR OF LEADS CONNECTABLE AT ONE END TO ONE OF SAID PAIRS OF CONDUCTORS OF SAID CIRCUIT TO PROVIDE AN INPUT TERMINUS, (2) A FIRST TRANSFORMER CONNECTED BETWEEN SAID LEADS, (3) A SECOND TRANSFORMER CONNECTED BETWEEN SAID LEADS AT THE OTHER ENDS THEREOF, (4) A FIRST RESISTOR CONNECTED IN SHUNT ACROSS SAID LEADS AT A LOCATION BETWEEN THE TRANSFORMERS, (5) A PAIR OF SECOND RESISTORS CONNECTED IN SERIES IN EACH OF SAID LEADS AT A LOCATION BETWEEN SAID SHUNT AND THE SECOND TRANSFORMER, (6) A PAIR OF FIRST AND A PAIR OF SECOND RECTIFIERS CONNECTED IN SHUNT ACROSS SAID LEADS AT A LOCATION BETWEEN THE SERIES-CONNECTED RESISTORS, THE FIRST RECTIFIERS HAVING THEIR NEGATIVE TERMINALS CONNECTED TO THE RESPECTIVE LEADS AND THE SECOND RECTIFIERS HAVING THEIR POSITIVE TERMINALS CONNECTED TO THE RESPECTIVE LEADS, AND (7) A CONNECTION EXTENDING TO GROUND FROM A LOCATION BETWEEN THE SECOND RECTIFIERS; 